High-Contrast Imaging and the Direct Detection of Exoplanets

Sandrine Thomas, Ruslan Belikov, and many collaborators

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Is there another Earth out there?

Is there life on this over Earth?

Requirements for habitability

1. Planet size:~ 0.5 – 2 Earth size

2. Temperature:0-100 C

3. Biomarkers: water and oxygen 3

not habitable(too large, hydrogen gas does not escape)

habitable

not habitable(too small to keep oxygen and water)

H2O(Water)

O2

(Oxygen)

(Schematic representation only)

Credit: Petigura/UC Berkeley, Howard/UH-Manoa, Marcy/UC Berkeley

Ref: R. Hanel, GSFC

O2

Iron oxides

CO2

H2O H2O

CO2

EARTH-CIRRUS

VENUS

X 0.60

MARS

EARTH-OCEAN

H2O H2O

H2O ice

O3O2

Spectroscopy: detecting biomarkers

Detecting atmospheric oxygen and water likely indicates life(because very few non-biological processes can sustain an oxygen atmosphere)

861 confirmed planets (677 planetary systems)2740 planet candidates (from Kepler mission)

Wobble method #1: Radial Velocity(Wobble method #2: Astrometry)

Direct detection

Direct ImagingMain Engineering Requirements

• Contrast– ~1010 for Earth-like planets– ~107 for young hot planets and disks

• Inner Working Angle– The smaller the better!– Typically 1-3 l/D required on missions

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2010 2020

Kepler

2030

Exo-C/S or AFTA(~1.4m / 2.4m,$1B / $2B+)

New WorldsTelescope($4-8m, $4B+)

Beyond Kepler: Direct imaging missions

Small sats(0.25-0.7m,~$5 – 200M)Earth-sizeHabitable zoneSpectroscopyTwo stars: aCen

Earth-sizeHabitable zoneNo spectroscopy (biomarkers)Not nearby systems

Earth-sizeHabitable zoneSpectroscopy~100s of Earths

All these missions also do ground-breaking science on non-habitable planets

Earth-sizeHabitable zoneSpectroscopy~6-20 stars

Another Earth?

Simulation of an exo-Earth around aCenwith a $1B mission (1.5m telescope)

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Ground based Instruments:Exoplanet direct imaging instruments

SPHERE

GPI

P1640 SCExAO

Beuzit et al, 14

Hinkley et al, 08 Guyon et al, 10

Macintosh et al, 14

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High Contrast Imaging

Like searching for a firefly next to a lighthouse in San Francisco from Boston=> Very faint and small in comparison

Upper Scorpius Lafreniere et al 2008

Beta Pictoris b Lagrange et al 2010

HR 8799 Marois et al 2008

Fomalhaut b Kalas et al 2008

Limitations• Diffraction from the parent star

– Depends on telescope diameter and wavelength: FWHM=lambda/d

• Passives and active aberrations in the system – Constant: static aberrations of the system – 1Hz: drifts due to temperature, flexure,

mechanical instability.– 1KHz: from the ground: atmosphere

• Amplitude errors and Talbot effect that turns amplitude errors into phase errors 1 nm RMS non-

common path WFE

5 nm RMS non-common path WFE

Solutions• Diffraction: Coronagraphs• Aberrations: Active and adaptive optics

– Wavefront sensor : Shack-Hartmann, curvature sensors– Deformable mirror– Control software

fromtelescope DM system Coronagraph

Science camera

WFS Starlight rejectedby coronagraph

feedback

Diagram of a direct imaging instrument

feedback

The Lyot CoronographSivaramakrishna, 2001

Principle of Pupil Apodization-type coronagraphs

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Image plane

starlight

Telescope pupil Resulting image

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Apodizer manufacture:halftone technique using black chrome microdots

by JenOptiks.

The apodizer transmission is obtained by randomly distributing 2μm square dots over the glass.

The Apodized Lyot coronagraph

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Pupil plane Focal plane Lyot stop ImageAime et Al. 2001

Challenge #2: optical aberrations

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Image plane

starlight

Telescope pupil Resulting image

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Adaptive Optics System for Turbulence Correction

WFSFeedback

Imager

DM

Distorted wavefront

Corrected wavefront

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Image sharpening for slow changing aberrations

WFS

Feedback

Imager

DM

Distorted wavefront

Corrected wavefront

Speckle Nulling

• We need to know how the DM phase maps to the image location and intensity• To calibrate location drive the DM at the highest spatial frequency• To calibrate the intensity measure some of the spatial frequency and interpolate the

rest

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Lab Performance after Speckle Nulling

Savransky, Thomas et al., 2012

Before static wavefront correction

After static wavefront correction

Example: Gemini Planet Imager, Macintosh B.

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Image Sharpening: Ex: Electric Field Conjugation (Give’on et al. 2008, Thomas et al. 2010)

- Calculate the electric field (Ef) in the focal plane- Find the DM shape such that its effect in the plane of interest

negates the electric field present in this plane- Possible to correct both phase and amplitude

G A + Ef = 0

Actuator commands

Electric field in the focal plane

Reconstruction matrix Improves the contrast by a factor 3,

reaching 4.10^8.

The Ames Coronagraph Experiment (ACE)

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The Ames Coronagraph Experiment (ACE) Laboratory

MEMS from Boston Micromachine Corporation

On stepper and piezo stage

• Cooling system• Wavefront Control: SN, EFC, LOWFS

People and organizations partnering with ACE

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NASA ARCRuslan BelikovThomas GreeneEugene PluzhnikSandrine ThomasFred WittebornDana LynchPaul DavisEduardo BendekKevin Newman

UofAOlivier GuyonGlenn SchneiderJulien Lozi

JPLBrian KernAndy KuhnertJohn TraugerWes TraubJohn KristMarie LevineStuart ShaklanK. Balasubramanian

Lockheed MartinDomenick TenerelliRick KendrickAlan DuncanWes IrwinTroy Hix

PrincetonJeremy KasdinBob VanderbeiDavid SpergelAlexis Carlotti

L3 TinsleyJay DanielAsfaw BekeleLee DettmannBridget PetersTitus RoffClay Sylvester

STScILaurent Pueyo

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Contrast Achieved in air

Median contrast of 4.06x10-7 between 1.2 and 2 l/d Simultaneously with 8.51x10-8 between 2 and 4 l/d

Mask Inner Working Angle (IWA)=1.12 λ/dAverage over an hourSpeckle nulling, round mask

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Stability

- Contrast remains under 10-6 in the inner region and under 10-7 in the outer region for over an hour, (represented as 1500 images).

- Same performance was obtained in three independent tests.

- Reapplying a MEMS map 1-day after the correction without changing the calibration keeps the results within 10%.

=> MEMS stable and reproducible correction

Vacuum tests• We achieved the same contrast as in air, but on

a bigger zone: 1.2-12 λ/D instead of 1.2-4 λ/D• We are close to the milestone in polychromatic

(1.8e-7 at 5%, 3.2e-7 at 10% between 2 and 12 λ/D)

• Limited now by a manufacturing default of the focal plane mask (OD3 instead of OD5)

• A new mask will be manufacture for the last vacuum test, and help us achieve the milestone.

Monochromatic result

Focal plane mask

Polychromatic result with bandwidth of 5, 10, 20 and 40 %.

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Status/Next steps Milestone #1 demonstration requirement met (exceeded) in air

1.8e-7, 1.2-2.0 l/D simultaneously with 6.5e-8, 2.0-4.0 l/D

First vacuum tests started in January and are ongoing

Milestone #2 (10% broadband light) to be pursued this year

EXCEDE aggressive IWA technology development can be beneficially carried over to future larger scale coronagraphic missions with focus on exoplanets

Most of the credit goes to: J. Lozi: LOWFS, DAQ, system calibration S. Thomas: Optical design, EFC wavefront control E. Pluzhnik: Optical assembly and alignment, SN E. Bendek: CAD design and layout T. Hix and the rest of the LM team: Vacuum hardware preparation and chamber operations

Adaptation to halo beam issues

• Figure 1. Lower-dynamic-range transverse beam profile measured in Jefferson Lab’s free-electron laser injector. The blue halo intensity is about 300 (arbitrary units) less than that of the green core. Image courtesy of Pavel Evtushenko

Will need: • Contrast needed? 1e-7?• How far from the core

do you need to observe?• Which wavelength?• Dynamic range of the

detector

Potential issues:- Static and dynamic

aberrations (Stability?)- The source is resolved.- The source size varies

with time (how much?)- Noise- Mie scattering?

Christine Herman, 2001

Christine Herman, 2001 Need contrast of about 1e-4/1e-5?

Conclusion

• Similar issues are seen by your groups and coronagraphy for astronomy.

• Need a translation between astronomy and particle physics

GPI Observations of HR 4796A

Individual 60 s imagesOne linear polarization shown.Waveplate rotates 0, 22.5, 45...& the parallactic angle changes

Combined 12 minutesTotal intensity

Combined 12 minutesLinear polarized intensity

N

E0.5”